Oil-containing polyester coating

ABSTRACT

A hard, flexible modified polyester coating is formed from a polyester resin which is made by (1) heating a mixture of a fat and a triol preferably in the presence of a catalyst until the ensuing transesterification reaction is substantially complete and (2) heating the product of (1) with a diol and a combination of aromatic and aliphatic polybasic carboxylic acids until the latter reaction is substantially complete. This polyester resin is blended with an aminoplast resin to produce a modified polyester resin composition which cures to a hard, yet flexible coating. Additional triol may be included in step (2). The weight of each of the above components in the total reaction mixture (1) plus (2) is: fat 20-25 percent; polyol 30-40 percent with the amount of triol comprising 45-70 percent of the polyol; and polycarboxylic acids - 40-56 percent with the aromatic polycarboxylic acid constituent comprising 83-92 percent of the polycarboxylic acid constituent.

O Unlted States Patent 1 1 1111 3,714,091

Lasher 1 1 Jan. 30, 1973 [54] OIL-CONTAINING POLYESTER COATING PrimaryExaminerDonald E. Czaja Assistant Examiner-Ronald W. Griffin [75]Inventor. gglyytard A. Lasher, Beverly Hills, Atmmey D0nald E- Nist andy H. Quartz [73] Assignee: Whittaker Corporation, Los An- [57] ABSTRACTgekis A hard, flexible modified polyester coating is formed [22] Filed:March 22, 1971 from a polyester resin which is made by (l) heating amixture of a fat and a triol referabl in the resence [21] Appl' 126951of a catalyst until the ensuiri g transes terificati on reaction issubstantially complete and (2) heating the [52] US. Cl. ..260/21,117/132 B, 117/161 K, product of (l) with a diol and a combination ofaro- 117/161 LN, 260/22 R, 260/22 M, 260/22 matic and aliphaticpolybasic carboxylic acids until CQ, 260/22 XA, 260/33.4 R, 260/33.6 Rthe latter reaction is substantially complete. This [51] Int. Cl. .Q..C09d 3/52, C09d 3/66 polyester resin is blended with an aminoplastresin to [58] Field of Search .....260/21, 22 R, 22 CO, 22 XA, produce amodified polyester resin composition which I v 260/22 M cures to a hard,yet flexible coating. Additional trio] 1 may be included in step (2) Theweight of each of the [56] References Cited above components in thetotal reaction mixture (1) plus (2) is: fat 20-25 percent; polyol 30-40percent UNITED STATES PATENTS with the amount of triol comprising 45-70percent of 3,325,428 6/1967 Graver et a1 ..260/22 the p y andpolycarboxylic acids 40-56 P 3,557,691 1/1971 Bayer ..101 129 wit thearomatic polycarboxylic a d constituent 3,575,901 4/1971 Ashjian..260/22 comprising 83-92 percent of the polycarboxylic acid 3,223,65812/1965 Kraft et al. ..260/22 constituent, 2,609,348 9/1952 Du .Puis eta1. ...260/22 3,467,610 9/1969 Fiarman et al. ..260/22 10 Claims, N0Drawings OIL-CONTAINING POLYESTER COATING BACKGROUND OF THE INVENTIONThis invention relates to polyester resins and to paints made therefrom.

At present, it is common practice to ship metallic sheets havingthicknesses less than about 0.1 inches from mills in coil form topreserve space. Some end uses of the metal sheets require coating orpainting of the metal. Such coating can be performed after the metal hasbeen sized and formed into the end product. However, this can beexpensive since the coating of in dividual products does not lend itselfto production line techniques, particularly if the product designinvolves complex shapes. Therefore, the coating operation is presentlyperformed by passing the coiled metal sheet through a machine whichfirst unwinds the coils, cleans and coats the flattened sheet, bakes thecoated sheet to cure the coating and, thereafter, re-coils the coatedsheet for shipment to a fabricator. The latter cuts and forms the coatedmetal sheeting into such diversified products as home siding, awnings,and bottle caps. The re-coiling and subsequent fabrication steps subjectthe coatings on the metal sheet to'severe treatment including complexbending of the metal and substantial pressure, particularly when themetal is coiled.

As is apparent from the foregoing, the coating material must be hard inorder to withstand high pressures without marking and it must also havesufficient flexibility to bend with the metal without cracking orpeeling away from the metal. Additionally, the coating composition mustbe capable of being readily and uniformly applied to the metal substrateeven though coil coating line conditions such as temperature, airflowand solvent concentration may change.

At pr'esent, a number-of different types of compositions are available.However, each has several disadvantages and, thus, none of thesecompositions presently satisfies the aforementioned coating propertiesrequirements. Forexample, both oil-free and dimer acid modifiedpolyester coating compositions ,are available but their use is generallyresisted by major coil coaters because. coatings produced from thesepolyesters have a significant tendency to show flow patterns, craterdefects and minute wrinkles. These film defects result from the highsensitivity of these polyesters to even small changes in 'coil coatingline conditions. This sensitivity, in turn, results from the need to usestrong solvents or solvent systems with these polyesters. The use ofstrong solvents is characterized by a significant reduction in the rangeof operating conditions within which satisfactory coating can beobtained. If, for example, a small amount of a strong solvent is lostdue to evaporation, the polyester coating will often exhibit theaforementioned coating defects due to poor solvation. If additionalsolvent is used to anticipate such losses, similar defects usuallyresult because of too low viscosity.

As usedherein, the terms strong" and weak" solvents are used todesignate hydrocarbon solvents having kauributanol values (KB values) of90 and higher, and less than 90 and above about 70, respectively.

Although the oil-free polyester resins, in particular, exhibitsatisfactory hardness and flexibility, the aforementioned applicationdisadvantages have caused many coil waters to use other coatingcompositions such as alkyd-amino and acrylic-amino compositions.However, these compositions are not completely satisfactory because theydo not exhibit the requisite hardness and chemical resistance.

SUMMARY OF THE INVENTION cluded in the latter step. The weight percentof each of the aforementioned components in the total reaction mixtureinvolved in the foregoing steps is: fat about 20 percent to about 25percent; polyol about 30 percent to about 40 percent with the amount oftriol comprising about percent to about 70 percent of the polyol; andpolycarboxylic acids about 40 percent to about 56 percent with thearomatic polycarboxylic acid constituent comprising about 83 percent toabout 92 percent of the polycarboxylic acid constituent.

The polyester resin product from the foregoing reaction may be employedalone as a coating or it may be modified by blending it with smallamounts, e.g., 8-20 percent by weight, of an aminoplast resin which actsas a cross-linking agent. The coatings may also be pigmented as desired.

The modified polyester coatings of this invention yield a film, whencured, that has excellent mar resistance and hardness with goodflexibility. Additionally, the cured coatings are substantially freefrom staining by such materials as mustard, ballpoint pen ink, road taroil, tobacco tars, tincture of iodine, and lipstick.

Furthermore, the modified polyester resins of this invention, prior tocuring, are easy to handle and can be readily applied to substrates. Thepolyester resins are readily soluble in solvents having KB values as lowas -75. For this reason, these resins can be readily applied to asuitable substrate, even though line conditions may change, withoutproducing the film defects which result from use of strong solvents withprior art polyesters when the same changes in line conditions occur.

DESCRIPTION OF THE PREFERRED EMBODIMENT All percentages used herein andin the claims are percentages by weight. Additionally, unless otherwisespecified, all concentrations are given as a percent of the totalreaction mixture weight employed in forming the herein-describedpolyester resins (excluding solvents).

In general, the herein-described polyester resins are formed by firstreacting at elevated temperatures, a fat with a triol, in the presenceof a catalyst, until the resulting transesterification reaction reachesthe desired stage of reaction and, thereafter, reacting the resultingproduct with a diol and with a combination of aromatic and aliphaticpolycarboxylic acids, at an elevated temperature, until the latterreaction is substantially complete. In each step, specific amounts ofeach of the constituents are employed in order to obtain polyesterresins having substantially improved characteristics as compared withpresently-employed coatings. Further improvements may be obtained bycross-linking the polyester resins formed as described above, with smallamounts of an aminoplast resin.

The particular combination of components, used in the concentrationranges described herein, produces cured polyester resins which,particularly when reacted with small amounts of a cross-linking agent,are hard (2l-1-3aH pencil hardness), flexible (1T 180) and stainresistant. Additionally, the resins, prior to cure, are readily solublein weak solvents having KB values of 70-75. If any of the componentsemployed herein is used in concentrations outside the ranges set forthfor that component or completely omitted, one or more of the foregoingcharacteristics will be adversely affected. This is because theparticular components, in the given concentration ranges, bothsupplement and offset the contributions of the other components. Forexample, the flexibility of the cured polyester is primarily obtainedfrom both the fat and the aliphatic polycarboxylic acid, solubility inweak solvents is primarily obtained from the fat and totalpolycarboxylic acid, and hardness is largely dependent upon the aromaticpolycarboxylic acid. Thus, it will be understood that, by changing theamount of one component to enhance a particular characteristic, anothercharacteristic may be adversely affected.

The polycarboxylic acid constituent employed herein is a mixture of oneor more aromatic polycarboxylic acids with one or more aliphaticpolycarboxylic acids. As used herein, the term polycarboxylic acidrefers to the acids themselves as well as to the correspondinganhydrides of such acids. The aromatic polycarboxylic acids include:orthophthalic acid, isophthalic acid, terephthalic acid,tetrahydrophthalic acid, hexahydrophthalic acid and endomethylenetetrahydrophthalic acid. Halogenated derivatives of the aforementionedpolycarboxylic acids and anhydrides may also be employed herein. Thelatter derivatives include, for example, tetrachlorophthalic acid andtetrabromophthalic acid.

The aliphatic polycarboxylic acids employed herein have from three to 18carbons and include: malonic acid, succinic acid, glutaric acid, adipicacid, suberic acid, azelaic acid, trimethyl adipic acid, sebacic acidand dodecenyl succinic acid. Adipic acid is presently preferred becauseof its low cost, availability and the excellent results obtained fromits use.

The concentration of the polycarboxylic acid component in the reactionmixture varies between about 40 percent and about 56 percent. Belowabout 40 percent, both the hardness and chemical resistance of the curedpolyester resins are substantially reduced. Above about 56 percent,there is a significant loss in flexibility. That is, embrittlementoccurs with the result that cracking of the coatings occurs when theunderlying substrate is bent.

The concentration of the aromatic polycarboxylic acid moiety in thepolycarboxylic acid mixture varies between about 83 percent and about 92percent with the remainder of the polycarboxylic acid component beingthe aliphatic moiety. Below about 83 percent by weight of aromaticpolycarboxylic acid, hardness is lost whereas, above about 92 percent,flexibility is lost.

The polyol derivative of this invention comprises the combination of oneor more triols with one or more diols. Triols which may be used includethe following: glycerine, trimethylol ethane, trimethylol propane,trimethylol butane, hexanetriol, and pentanetriol. Useful diols includethe following: ethylene glycol, 1,2, and 1,3 propylene glycol, 1,3 and1,4 butylene glycol, 1,5 pentane diol, 1,6 hexanediol, cyclohexanedimethanol, 2-ethyl,2-methyl, 1,3 propane diol, neopentyl glycol,diethylene glycol, and dipropylene glycol.

The amount of polyol employed is primarily dependent upon the amount ofpolycarboxylic acid in the reaction mixture. An amount of polyol is usedwhich is sufficient to substantially completely esterify thepolycarboxylic acid. 1f substantial amounts of polycarboxylic acidremain unreacted (with respect to the polyol), the improved hardness andflexure properties characterizing the cured resins of this inventionwill not be obtained. Therefore, at least a stoichiometric amount ofpolyol is employed. Preferably, about 20 percent excess polyol isemployed. The use of higher amounts of polyol results in cured resinshaving relatively poorer exposure properties. In view of the foregoing,the amount of polyol varies between about 30 percent and about 40percent.

The trio] fraction of the polyol component varies between about 45percent and about percent of the weight of the polyol derivative withthe remainder being diol. Below about 45 percent of trio] in the polyolderivative, the cured polyester resin is characterized by being softerand having poorer chemical (stain) resistance. Above about 70 percent oftriol, embrittlement occurs and the resin viscosity increases to theextent that gellation occurs before the esterification end point isreached.

The fats employed herein are usually of vegetable origin although theymay be of animal origin, e.g., beef tallow. Although fish oils could beused, their odor usually precludes such use. As used herein, the termfat" designates triesters of fatty acids, e.g., triglycerides, andincludes both saturated and unsaturated types. In the latter form, theyare often referred to as oils. Any of the unsaturated fats may behydrogenated. The term fat includes both naturally occurring andsynthetic (synthesized from fatty acids and triols) compounds. In resinpreparation, it is particularly useful to use hydrogenated or saturatedfats to obtain improved color retention.

Oils which may be employed in this invention include: soyabean,safflower, sunflower, walnut, dehydrated castor, olive, peanut, rawcastor, coconut, and linseed. lsomerized versions of these oils may alsobe employed. For example, conjugated safflower and sunflower oils may beused. Combinations of these oils may also be employed. These oils may beused in their unbodied form or the heat-bodied, unsaturated oils may beemployed with Gardner-Holdt viscosities as high as Q althoughGardner-Holdt viscosities of F to H are preferred. Examples of theheat-bodied oils include soyabean, safflower, sunflower, walnut,dehydrated castor and linseed oils. Both bodied and unbodied oils may beused together.

The concentration of the fat in the reaction mixture varies betweenabout 20 percent and about 25 percent. Below about 20 percent, theuncured polyester resin is not sufficiently soluble in weak solvents tobe commercially useful. Above about 25 percent, the cured polyesterresin does not have sufficient hardness.

As previously mentioned, it is preferable to employ a catalyst to speedup the initial transesterification reaction without using excessivelyhigh temperatures. Useful catalysts include Ca(OH) NaOl-l, KOH, LiOlland PbO.

The method employed to produce the polyester resins of this inventionfrom the foregoing constituents is well-known in the art and will now bebriefly described. The presently preferred preparation of the polyesterresins involves a two step process in which the first step involves thereaction of the fat with the triol. This is accomplished by heating afirst reaction mixture of the fat and triol, in the amounts previously.set forth and preferably in the presence of a catalyst such as lithiumhydroxide'monohydrate, to a temperature preferably between about440F andabout 480F. The particular temperature chosen is primarily a function ofthe time required to complete the reaction with the reaction timedecreasing with increasing temperature. Preferably, to avoid oxidationof the reactants and product, the reaction is performed in an inertatmosphere. This may be accomplished by bubbling an inert gas such asnitrogen or carbon dioxide through the reaction mixture. The reactionmixture is stirred to obtain substantially uniform mixing and is held atthe elevated temperature to which it is raised until the required degreeof transesterification has been reached. The degree or state of thetransesterification reaction can be determined by checking thesolubility of the mixture in methanol. The required degree oftransesterification is obtained if one volume of the reaction mixture toa minimum of four volumes of methanol gives a clear solution at roomtemperature.

When the reaction is complete, heating is discontinued and the reactionmixture is allowed to cool to a temperature which is dependent upon theoperating conditions. For example, if the reaction vessel is open to theatmosphere, cooling continues until a temperature is reached at whichsignificant oxidation does not occur. If the vessel is sealed to theatmosphere, no cooling is required. At this point, the remainingreactants, including the diol and the polycarboxylic acid, are added tothe product of the first reaction mixture, preferably together with asolvent to facilitate interaction of the constituents in this secondreaction mixture. Additional triols may also be added at this point.This second reaction mixture is then slowly heated to a temperaturepreferably between about 420F and about 470F and held atthis temperaturefor a time sufficient to substantially complete the reaction. As withthe first reaction, the temperature chosen for the second reaction isprimarily dependent upon the time required to completethe reaction. Thedegree of completion of the reaction can be determined by making a 50percent solution of the reaction solids in xylene and determining theviscosity of this solution. In general, the reaction will besubstantially complete if the Gardner-l-loldt viscosity of this solutionis at least Q viscosity (50 percent solution in xylene) and, preferably,between S and U with an acid number preferably below 10. The resultingreaction mixture may then be thinned to a desired solids content withany appropriate solvent.

The solvents employed during the course of the reaction may include, forexample, xylene, toluene, benzene and cyclohexanone. The solventsemployed to thinthe resulting reaction product may include, for example,any of the foregoing solvents as well as Amsco solvent 13-65 with aboiling range of 158 to C and kauri-butanol value of 72, Amsco solvent Fwith a boiling range of 183 to 206C and a kauri-butanol value of 74,Amsco solvent G with a boiling range of 184 to 209C and kauri-butanolvalue of 90, Amsco solvent HC with a boiling range of 241 to 275C and akauributanol value of 98.

The polyester resins made as described above, may be used unmodified or,preferably, modified with am inoplast resins to cause cross-linking ofthe polyester chains by well known methods to produce hard, yet flexiblecoatings. The aminoplast resins include, for example, butylatedurea-formaldehyde resins, butylated melamine-formaldehyde resins,hexamethoxymethylmelamine or mixtures of varioushydroxymethylmelamine-methyl ethers such as thepentamethyoxymethylmelamine and the tetramethoxymethyl melamines. Thehydroxymethylmelamine and hydroxymethyl ureas may also be etherifiedwith alcohols other than methyl or butyl such as ethyl, propyl, isobutyland isopropyl. Preferably, hexamethoxymethylmelamine alone or incombination with butylated melamine resin is employed. The amount ofaminoplast employed with the polyester resin is less than about 20percent of the weight of total resin solids in the mixture. Above about20 percent, the cured resin is too brittle. The aforementioned preferredaminoplast resin is preferably used in the range of 8 to 14 percent oftotal resin solids whereas butylated melamine, which has a higher etherlinkage content is used in amounts near the 20 percent limit.

This invention will now be further described by the following Examples.In each of these Examples, the term parts is parts by weight.

EXAMPLE 1 Polyester resins (D-G) were made using the components andconcentrations shown in Table 1 and using the following procedure ineach case.

To a reaction vessel which was suitably equipped with heater, inert gasconnections, stirrer, thermometer and condenser, there was initiallyadded the vegetable oil, some or all of the triol and 0.35 parts byweight of iithium hydroxide monohydrate as catalyst. 1n the initialmixtures for D and E, 273 parts of triol were used, for F, 293 parts oftriol were used, and for G, all the triol was used. A stream of carbondioxide gas was TABLE 1 Component or Amount (parts by wt.) Property D EF G blpn-break soyabean 510 490 01 G viscosity soya- 510 bean oil G-Hviscosity 490 dehydrated castor oil Trimethylol ethane 454 456Trimethylol propane 514 514 Phthalic anhydride 864 859 880 860 Neopentylglycol 224 261 262 262 Adipic acid 70 75 75 v 95 acid number 8.4 8.9 9.07.2 final viscosity U Z W U Paints l-l-K were made from the polyesterresins D-G, respectively, as follows. In each case, 11.6 parts of thepolyester resin, thinned to 60 percent solids as described, was combinedwith 24 parts of titanium dioxide and 6.6 parts of Amsco G solvent in aball mill and blended until the desired particle size was obtained. Tothe resulting mixture, there was added with stirring 38.7 parts of thesame polyester resin, 6.8 parts of 50 percent'hexamethoxymethylmelamine, 1.5 parts of butylated melamine, 5.0 parts of Amsco solventBC, 1.8 parts of 13 percent wax solution, 4.0 parts of Amsco G solventand 0.3 parts of 1010 catalyst (para toluene sulphonic acid 20 percentsolution in ethanol).

The resulting paints H-K were each applied to a primed aluminum paneland hardened by heating at 550F for 1 minute. The cured paints weretested for hardness (pencil) and for chemical resistance to a 2 percentiodine solution (after 24 hrs.) and to MEK (1 min. 120 rubs). The testresults are shown in Table 11.

The flexibility of these paints (H-K) was also tested on thin aluminumsheet and they readily passed a 1T180 bend without cracking. Thesepaints therefore show that a high hardness (2H) is obtainable withexcellent flexibility when employing the components and concentrationsdescribed herein.

EXAMPLE 2 Polyester resins (L-P) were made up using the proceduredescribed in Example 1 for resin G. The particular components andconcentrations employed are set out in Table 3.

TABLE 3 Component or Amount (parts by wt.) Property M N O G viscositysoya- 490 490 490 490 bean oil Raw castor oil 490 Phthalic anhydride 860860 860 860 lso-phthalic acid 963 1,4 cyclohexane 363 dimethanolNeopentyl glycol 433 262 262 Diethylene glycol 26 7 Adipic acid 95 95Sebacic acid l37 Trimethylol propane 514 374 514 514 514 Acid number 9.09.5 7.4 10.2 9.0 Final viscosity U- T+ U V- T- (50% in xylene) As willbe noted from Table 3, resin L was made using 1,4 cyclohexane dimethanolas the diol rather than neopentyl glycol; resin M was made usingisophthalic acid for the aromatic dibasic carboxylic acid component andthe amount used produced a diol/triol ratio in the low end of the rangerequired in this invention; resin N was made using sebacic acid ratherthan adipic acid; resin 0 was made using diethylene glycol as the diolcomponent; and resin P was made using raw castor oil as the vegetableoil.

Paints (Q-U) were made up and cured using each of the resins L-P,respectively, as described in Example 1 (same component concentrationsand same components except for the polyester resin). The hardness andchemical resistance of the cured paints is shown in Table 4.

Again, these paints were tested for flexibility and were found toreadily pass a 1T-l80 bend test.

EXAMPLE 3 A polyester resin (V) of this invention was made up asdescribed for resin G of Example 1 except that G viscosity safflower oilwas used in place of the G-l-l viscosity dehydrated castor oil of resinG. This resin (V) was then used to make a lb. batch of paint using theprocedure described in Example 1 but using the components and amountsshown in Table 5.

TABLE Amount Component 27.5 Titanium dioxide (Dupont R-966) tion Thispaint was employed in a conventional coil coating line to coat 5010aluminum alloy 13 in. wide X 0.019 in. thick. The paint applied welland, after curing, resulted in a high gloss film without surfacedefects. It had a 2H pencil hardness and its flexibility was sufficientto pass a l-T 180 bend. In contrast to many polyester coatingscross-linked with hexamethoxymethylmelamine and catalyzed withparatoluene sulphonic acid, this paint formed very wall on the l-T 180bend and did not subsequently develop fissures at the bend which cancurl back to produce a failure at the bend.

EXAMPLE 4 Both alkyd A and alkyd B resins were used to make paints usingthe method described in Example 1 for the preparation of paint H fromresin D. The particular ture consisted of 277.32 parts of 6-1-1dehydrated castor oil, 315.85 parts of trimethylol propane and 0.1 partof lithium hydroxide mono hydrate. The constituents added to the firstreaction product consisted of 36.97 parts of benzoic acid and 369.76parts of phthalic anhydride.

For the alkyd A resin, the second step reaction was continued until a 50percent solution of the alkyd resin in xylene reached a viscosity of T+.The properties, as determined in Example 1, were as follows: finalviscosity Z2; and acid number on solids 8.0. Thealkyd B second stepreaction was continued until a 50 percent solution of the resin inxylene reached a viscosity of V. The properties, as determined inExample 1, were as follows: final viscosity Z3; and acid number onsolids 8.0.

The compositions of both alkyd A and alkyd B fell outside the scope ofthis invention. For example,

neither alkyd resin contains an aliphatic dicarboxylic acid.Additionally, the component percentages in these resins are as follows:alkyd A oil-30 percent; polyol 30.5 percent with the trio] constituting75 percent of the polyol; and dicarboxylic acid (only aromatic) 40percent. Alkyd B contains 28 percent oil, 32 percent polyol (solelytriol) and 37 percent dicarboxylic acid (solely aromatic) together with3.7 percent mono carboxylic acid.

components and concentrations employed to make the paints are set forthin Table 6.

TABLE 6 Amount (1b.) Component Alkyd A Alkyd B Titanium dioxide 64.24(1.93 gal.) 64.24 Alkyd A 23.34 (2.8 gal.) Alkyd B 23.34 (2.75 gal.)Amsco G solvent 12.42 (1.68 gal.) 11.18 Butanol 1.24 Alkyd A paste 39.00Alkyd B paste 37.48 Alkyd A 49.00 Alkyd B 49.6 Butylated melamine (PR269- 7.70 7.64 solids) I Amsco G solvent 2.0 3.50 Butanol 1.3 0.24 15%wax solution 1.0 1.54

In the procedure employed in this Example, approximately 100 lb. of eachof alkyd A and alkyd B paste were made from the respective resin, TiOAmsco G solvent and butanol but lesser amounts of these pastes were usedtogether with the other components shown in Table 6 to make the paintformulations.

Each of the resulting'paints was tested for hardness, flexibility andchemical resistance. Their pencil hardness fell in the range I-lB-Fwhich is to be compared to the much higher 2H pencil hardness of thepaint of this invention described in Example 3. The flexibility of thealkyd A and B paints was comparable to that obtained for the paint ofExample 3. However, by lowering the hardness of the Example 3 paint ofthis invention, the flexibility can be made substantially superior tothe alkyd A and B paints. The stain resistance of the alkyd A and Bpaints was generally poor as they were substantially stained by iodine,lipstick, stencil ink, road tar and mustard. ln'comparison, the stainresistance of the Example 3 paint of this invention was very good sinceit showed substantially no staining under the same test conditions.

EXAMPLE 5 This Example illustrates the solubility of the hereindescribed polyester resins in a low KB solvent.

A polyester resin was made up using the following constituents andamounts: non-break soyabean oil (G body) 490 parts; trimethylol propane514 parts; lithium hydroxide monohydrate 0.35 parts; neopentyl glycol262 parts; phthalic anhydride 880 parts; and adipic acid parts. Theprocedure used was substantially the same as described in Example 1 forresin F. That is, the trimethylol propane was divided into two fractionsof 293 and 221 parts and the larger fraction was reacted in a firstreaction mixture with the oil and catalyst with the remainingtrimethylol propane included in the second reaction mixture. Thereaction was continued with the addition of xylol until a viscosity of Vwas obtained for a 50 percent solution of the resin in xylol.Thereafter, the reaction mass was thinned to 55 percent solids by theaddition of a solvent mixture containing 92 percent by volume of asolvent (35/42) having a KB value of about 75, 2 percent Amsco B and 6percent butanol. The latter was added primarily to obtain the desiredviscosity since the resin was sufficiently soluble in the 35/42 solventalone. The resulting resin solution had a viscosity of Z4 and an acidnumber of 8.0 on solids.

The resulting resin solution was employed to formulate a paint bycombining 10.15 parts of this resin solution with 25.3 parts titaniumdioxide and 12.2 parts Amsco G solvent in a sand mill to 7H grind. Allof the resulting paste was combined with 8.32 parts of butylatedmelamine solution (60 percent solids), an additional 42 parts of theresin solution, 1.53 parts of Amsco G solvent, 0.5 part ofwax, and 0.3parts of 1010 catalyst.

This paint was spread over a primed aluminum sheet to obtain a dry filmthickness of0.80 mils. Spreading of the paint was smooth and showed nocratering or other defects in spite of the presence of the low KB valuesolvent. The pencil hardness of the cured paint was l-l+. It showed noeffects following the previously-described iodine and MEK tests andeasily passed a lT-180 bend test. The paint of this Example was testedin Florida for exterior durability, i.e., durability to ultraviolet,temperature change, humidity and salt. lts exterior durability wasexcellent and was markedly superior to the prior art paints of Example 4when subjected to the same test.

When a paint was made as described except that hexamethoxymethylmelamine was used in place of butylated melamine, an increase inhardness (2H3l-l) was obtained with only a slight loss of flexibility(passed 1Tl80 bend test) as compared with the paint formulated withbutylated melamine. Thus, it will be understood that either the hardnessor flexibility of the paint can be enhanced by selection of theaminoplast resin. In any case, the combined paint hardness andflexibility characteristics are superior to those properties of theprior art paints.

1 claim:

1. The polyester resin which is obtained by heating the transesterifiedreaction product of (a) a fat and (b) a triol together with (c) a dioland (d) the combination of an aliphatic polybasic carboxylic acid havingfrom three to 18 carbon atoms and an aromatic polybasic carboxylic acid,each of components (a), (b), (c) and (d) being initially present in thefollowing weight percentages of the total weight of said components: (a)between about 20 percent and about 25 percent; (b) plus (c) an amountsufficient to completely esterify said (d) with said triol comprisingbetween about 45 percent and about percent by weight of said (b) plus(c); and (d) between about 40 percent and about 56 percent with saidaromatic polybasic acid comprising between about 83 percent and about 92percent by weight of said (d).

2. The polyester resin of claim 1 wherein said (b) plus (c) is presentin an amount between about 30 percent and about 40 percent by weight.

3. The polyester resin of claim 1 wherein said polybasic carboxylicacids are dibasic carboxylic acids or anhydrides thereof.

4. The polyester resin of claim 1 wherein at least one of said polybasiccarboxylic acids is halogenated.

5. The polyester resin of claim 1 wherein only a portion of said triolis resent in said transesterified reaction product and w erem theremainder of said triol 1S reacted with said transesterified reactionproduct and said (c) and said (d).

6. The polyester resin of claim 1 wherein said fat is selected from thegroup consisting of soyabean, safflower, sunflower, walnut, dehydratedcastor, olive, peanut, raw castor, coconut and linseed oils and tallow.

7. The polyester resin of claim 6 wherein said trio] is selected fromthe group consisting of glycerine, trimethylol ethane, trimethylolpropane, trimethylol butane, hexanetriol and pentanetriol.

8. The polyester resin of claim 7 wherein said diol is selected from thegroup consisting of ethylene glycol, 1,2 and 1,3 propylene glycol, 1,3and 1,4 butylene glycol, 1,5 pentane diol, 1,6 hexane diol, cyclohexanedimethanol, 2-ethyl, Z-methyl, 1,3propane diol, neopentyl glycol,diethylene glycol and dipropylene glycol.

9. The polyester resin of claim 8 wherein said aromatic polybasiccarboxylic acid is selected from the group consisting of orthophthalicacid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid,hexahydrophthalic acid, endomethylene tetrahydrophthalic acid, andwherein said aliphatic polybasic carboxylic acid is selected from thegroup consisting of malonic acid, succinic acid, glutaric acid, adipicacid, suberic acid, azelaic acid, trimethyl adipic acid, sebacic acidand dodecenyl succinic acid.

10. The polyester composition obtained by the reaction of the polyesterresin of claim 1 with an aminoplast resin in an amount less than about20 percent by weight of the total weight of resin solids.

1. The polyester resin which is obtained by heating the transesterifiedreaction product of (a) a fat and (b) a triol together with (c) a dioland (d) the combination of an aliphatic polybasic carboxylic acid havingfrom three to 18 carbon atoms and an aromatic polybasic carboxylic acid,each of components (a), (b), (c) and (d) being initially present in thefollowing weight percentages of the total weight of said components: (a)-between about 20 percent and about 25 percent; (b) plus (c) - an amountsufficient to completely esterify said (d) with said triol comprisingbetween about 45 percent and about 70 percent by weight of said (b) plus(c); and (d) - between about 40 percent and about 56 percent with saidaromatic polybasic acid comprising between about 83 percent and about 92percent by weight of said (d).
 2. The polyester resin of claim 1 whereinsaid (b) plus (c) is present in an amount between about 30 percent andabout 40 percent by weight.
 3. The polyester resin of claim 1 whereinsaid polybasic carboxylic acids are dibasic carboxylic acids oranhydrides thereof.
 4. The polyester resin of claim 1 wherein at leastone of said polybasic carboxylic acids is halogenated.
 5. The polyesterresin of claim 1 wherein only a portion of said triol is present in saidtransesterified reaction product and wherein the remainder of said triolis reacted with said transesterified reaction product and said (c) andsaid (d).
 6. The polyester resin of claim 1 wherein said fat is selectedfrom the group consisting of soyabean, safflower, sunflower, walnut,dehydrated castor, olive, peanut, raw castor, coconut and linseed oilsand tallow.
 7. The polyester resin of claim 6 wherein said triol isselected from the group consisting of glycerine, trimethylol ethane,trimethylol propane, trimethylol butane, hexanetriol and pentanetriol.8. The polyester resin of claim 7 wherein said diol is selected from thegroup consisting of ethylene glycol, 1,2 and 1,3 propylene glycol, 1,3and 1,4 butylene glycol, 1,5 pentane diol, 1,6 hexane diol, cyclohexanedimethanol, 2-ethyl, 2-methyl, 1, 3propane diol, neopentyl glycol,diethylene glycol and dipropylene glycol.
 9. The polyester resin ofclaim 8 wherein said aromatic polybasic carboxylic acid is selected fromthe group consisting of orthophthalic acid, isophthalic acid,terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid,endomethylene tetrahydrophthalic acid, and wherein said aliphaticpolybasic cArboxylic acid is selected from the group consisting ofmalonic acid, succinic acid, glutaric acid, adipic acid, suberic acid,azelaic acid, trimethyl adipic acid, sebacic acid and dodecenyl succinicacid.